1. Field of the Invention
The present invention relates to a non-magnetic toner for use in a recording method using an electrophotographic method, an electrostatic recording method, a toner jet method, or the like.
2. Description of the Related Art
In recent years, it has been strongly demanded that an electrophotographic apparatus such as a printer apparatus perform printing at an increased speed and be run at a reduced cost while achieving improvements in definition and quality of an image, and energy savings to an extent larger than the conventional one.
In association with such demand, characteristics requested of toner have become more and more sophisticated, and have covered a broader spectrum. Accordingly, attempts based on various viewpoints have been made on the development of the toner.
From the viewpoints of improvements in definition and quality of an image, a reduction in size of each particle of toner has been demanded in association with an increase in resolution of an image-forming machine up to, for example, 1,200 or 2,400 dpi. Production based on a polymerization method has been proposed as one method of producing the toner containing particles each having a reduced size. The toner based on the polymerization method is specifically obtained by the following method: a method involving the step of subjecting emulsified (agglomerated) resin particles and colorant particles to agglomeration and melt adhesion to prepare an amorphous toner (emulsified (agglomerated) toner) or a method of preparing toner particles (suspension polymerization toner) involving the steps of dispersing a radical polymerizable monomer and a colorant and subjecting the resultant to suspension polymerization by dispersing the droplets of the resultant in an aqueous medium or the like to obtain the toner having a desirable particle diameter so that toner particles are prepared.
In particular, in the case of the production of toner particles by the suspension polymerization method, each particle can be reduced in size with ease, and, furthermore, the resultant toner obtains uniform triboelectric charging performance because the toner shows a sharp particle size distribution and has a high sphericity, and the quality of a material for the surface of the toner becomes substantially uniform. As a result, a toner having high developing performance and high transferring performance can be obtained. In addition, a classifying step can be simplified because a sharp particle size distribution can be obtained as described above. Accordingly, the production of toner particles by the suspension polymerization method is preferable because of a large energy-saving effect, a large shortening effect on a time required for the production, a large improving effect on a yield in each step, and a large reducing effect on a cost for the production, from the viewpoint of a reduction in running cost.
Further, colorization has abruptly advanced in the field of electrophotography. Since a color image is generally formed by development with four kinds of color toners, that is, yellow, magenta, cyan, and black toners which are appropriately superimposed, each color toner is requested to have a higher developing characteristic than that in the case where the toner is used for the formation of a monochromatic image. That is, a toner having the following characteristics has been requested: an electrostatic image can be faithfully developed with the toner, the toner is transferred onto a transfer material such as paper with reliability while being prevented from scattering, and the toner is easily fixed to the transfer material. Such toner produced by the suspension polymerization method as described above is suitable from such viewpoint as well.
The development of a toner that is easily fixed to a transfer material such as paper at low temperatures has been demanded from an energy-saving viewpoint. In association with an improvement in resolution of an image, the control of the gloss value of the image upon formation of the image has been requested simultaneously with the above demand in order that the quality of the image may be brought close to that of a photograph or print. Further, in the formation of a color image, good color mixing performance and good color reproducibility over a wide range have been requested. For example, the acquisition of an image having such a high gloss value that the quality of the image is close to that of a photograph has been requested.
To cope with such request, the glass transition point (Tg) of a binder resin to be used in toner must be lowered, or the average molecular weight of the binder resin to be used in the toner must be lowered. However, in extreme cases, merely lowering the Tg or average molecular weight of the binder resin to be used in the toner impairs the storage stability of the toner to such an extent that an image cannot be obtained. In addition, particularly at the time of high-speed development or in the case of a non-magnetic, one-component developing system suitably applicable to a small apparatus with a low running cost, the toner is apt to collapse owing to a reduction in strength of the toner, so the contamination of a member due to the melt adhesion of the toner or to the exudation of a wax in the toner is apt to occur. As a result, it may become impossible to achieve the following object: an image-forming apparatus with a long lifetime and a low running cost. That is, when improving the fixing characteristic of the toner is simply attempted, the developing characteristic of the toner is impaired. In contrast, when the developing characteristic precedes the fixing characteristic, it may be impossible to improve the fixing characteristic. Although a reduction in average particle diameter of the toner is indeed effective means particularly from the viewpoints of improvements in definition and quality of an image as described above, the means unfortunately promotes the contamination of a member due to the melt adhesion of the toner or to the exudation of the wax, thereby making it additionally difficult to achieve compatibility between the low-temperature fixability and developing characteristic of the toner.
The achievement of compatibility between such properties of toner apparently contradictory to each other, that is, development stability and low-temperature fixability is an important problem which the toner is requested to tackle, and various proposals have been heretofore made on the problem.
For example, there has been proposal focused on the viscoelastic characteristics where viscoelastic characteristics in each of two temperature regions, that is, the temperature region of 60 to 80° C. and the temperature region of 130 to 190° C. can achieve the compatibility between low-temperature fixability and offset resistance (see Patent Document 1 and Patent Document 2).
Further, there has been disclosed that the compatibility between an additional improvement in fixability and developability can be achieved by specifying the local maximum value and local minimum value of a loss tangent (tan δ) as a ratio between a storage elastic modulus (G′) and a loss elastic modulus (G″) for the viscoelastic characteristics of toner (see Patent Document 3 and Patent Document 4).
However, each conventionally proposed technology is still susceptible to improvement in terms of the following point: while good fixing performance and high gloss are maintained, such damage to toner as described above is alleviated, and, for example, even when an increase in temperature inside a contact developing system due to continuous paper feeding in the system occurs, stable developing performance is obtained over a long time period.
[Patent Document 1] JP 09-34163 A
[Patent Document 2] JP 2004-333968 A
[Patent Document 3] JP 2004-151638 A
[Patent Document 4] JP 2004-264484 A